Nickel and cobalt are known as valuable metals and used for various applications in industry. Recently in particular, nickel and cobalt have been used in great amounts, for example, in positive electrode materials of secondary batteries such as nickel metal hydride batteries and lithium-ion batteries.
Nickel and cobalt can be obtained by melting, via a dry process, ores containing these in a furnace at a high temperature and refining the resulting intermediate such as the matte. In recent years, however, high-grade ores are almost exhausted and, as a result, a wet process called the HPAL process has been put to practical use. In the HPAL process, low-grade oxide ores that are not conventionally used much, such as laterite ores, together with a sulphuric acid solution, are placed in a pressure-resistant vessel within which the temperature and the pressure are then increased, and from the resulting leaching solution from which nickel and/or cobalt has leached out, nickel and/or cobalt or an intermediate containing these is retrieved. Because of its characteristics, the HPAL process allows highly efficient processing of low-grade nickel oxide ores having a nickel grade of 1 to 2% or lower that are not able to be processed by a dry method because of the low profitability.
In such ores, in addition to valuable resources (valuable components) such as nickel, cobalt, and scandium to retrieve, various impurities such as manganese, aluminum, zinc, iron, chromium, magnesium, copper, lead, sodium, lanthanum, neodymium, molybdenum, vanadium, tin, tungsten, samarium, rhenium, thallium, cerium, titanium, and lutetium are contained. These impurities can be relatively easily separated as slag by the dry process, while by the wet process, these impurities are often contained in the leaching solution together with valuable components such as nickel, cobalt, and scandium. For this reason, studies on separation of the impurities are required in order to obtain nickel, cobalt, and scandium from the nickel oxide ores.
As an alternative method, nickel and/or cobalt is recycled and retrieved from the used secondary batteries as mentioned above, waste electronic substrates, and the like. Positive electrode materials as constituents of the secondary batteries contain manganese as well as nickel and/or cobalt. In addition, the casings and the base materials contain aluminum, iron, and the like. Because of these and other reasons, separation between impurities and valuable resources has been left to be achieved even when recycling is adopted.
For example, as a common method of retrieving nickel as en end product, electrowinning to obtain metal is employed. In this method when manganese coexists with nickel, it is known that oxide of manganese becomes deposited on the surface of an anode used in electrowinning to accelerate anode degradation. Furthermore, colored fine oxide of manganese floats in the electrolyte solution to clog a filter cloth used in electrowinning, no cause contamination of the metal nickel with the oxide of manganese, or to cause another problem, and, as a result, quality decreases and consistent operation becomes hindered. Therefore, removal of manganese is a serious issue to resolve.
As a technique to remove manganese, precipitation is widely known (see Patent Document 1). Precipitation is a technique where pH adjustment of a solution containing nickel and/or cobalt and manganese is followed by addition of a sulphiding agent to obtain a precipitate of sulphide of nickel and/or cobalt or followed by addition of an oxidizing agent to obtain a precipitate of oxide of manganese.
It is also known that nickel oxide ores contain a trace amount of valuable scandium, but the scandium is not easily retrieved. For scandium retrieval, a method of leaching out nickel oxide ores with acid and then subjecting the solution from which nickel and the like have been retrieved to neutralization so as to retrieve scandium as a precipitate as in Patent Document 2, and a method of subjecting the solution to solvent extraction to separate scandium from other impurity components and then performing concentration as in Patent Document 3 are known, for example.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2000-234130
Patent Document 2: Japanese Unexamined Patent Application, Publication No. H09-143589
Patent Document 3: Japanese Unexamined Patent Application, Publication No. H09-291320